Simplified microwave repeater



Jan. 23, 1962 A. J. LlPlNSKI SIMPLIFIED MICROWAVE REPEATER Filed Oct. 30, 1959 Fig. I

3| l2 1 4 20 el 28 2 9 ll Low l3 Variable 30 Noise 8 Mi Power Klysiron r Wave Klystron Amplifier AHenuaior 32 T 33 I6 23 F 24 27 1 i l l 34 AF 35 I3 Generator Moving Servo And Means Amplifier 42 Modulator 25 26 I5 Utilization Circuit Basebond Channel x 4O lg. 2 "4' I WITNESSES |NVENTOR Andrew J.- Lipinski #10 2 mRNEY United States Patent Office 3,018,375 Patented Jan. 23, 1962 3,018,370 SIMPLIFIED MICROWAVE REPEATER Andrew J. Lipinski, Alberton, Ontario, Canada, assignor to Canadian Westinghouse Company, Limited, Hamilton, Ontario, Canada Filed Oct. 30, 1959, Ser. No. 849,933 7 Claims. (Cl. 250-15) This invention relates to improvements in repeaters, and more particularly to microwave repeaters.

In the present state of the repeater art the retransmission of signals at microwave relay stations is obtained by three distinct methods, which may be called the backto-back method, the heterodyne at intermediate frequency method, and the straight-through repeating method at radio frequencies. Present apparatus for obtaining microwave repeating by each of these three methods is bulky and complicated by reason of the necessity for obtaining the desired gain at the repeater station, which may be well over 120 decibels, the necessity for discriminating against unwanted signals, and the necessity for preventing spurious output signals.

Filtering and band-pass apparatus to meet the last two requirements increases the amplification which must be provided over the normal requirements.

Accordingly, a primary object of the instant invention is to provide a new and improved microwave repeater.

Another object is to provide a new and improved simpliiiecl wide band repeater for microwaves.

A further object is to provide a new and improved microwave repeater in which the necessity for elaborate frequency discriminating circuits is eliminataed.

These and other objects will become more clearly apparent after a study of the following specification when read in connection with the accompanying drawing, in which:

FIG. 1 is a schematic electrical circuit diagram in block form of the preferred embodiment of the invention; and

FIG. 2 is a detailed schematic showing the connections of the power klystron of FIG. 1.

in summary, the apparatus of the instant invention utilizes a power klystron in which the resonant characteristics of the cavities of the klystron are utilized to obtain band-pass characteristics and discrimination against unwanted signals, the klystron providing a large percentage of the total gain of the repeater circuit.

Referring now to the drawings for a more detailed understanding of the invention, and in particular to FIG. 1 thereof, there is shown a receiving antenna 10 of any convenient design for receiving a microwave signal of predetermined frequency. The output of the antenna 1% is supplied by conducting means which may be a waveguide 11 to a low-noise klystr'on amplifier shown in block form at 12. By suitable choice of a klystron tube and component values a gain of 30 decibels may be obtaned in the stage 12 while maintaining a very low noise level. The output of the klystron amplifier '12 is supplied by lead means 13 to a low level mixer stage shown in block form at 14. Mixers usually are accompanied by some loss in power level and a loss in the order of 8 decibels may be expected in the mixer 14; such a loss would not be considered excessive. The lead means 13 also provides a drop-out of channels in a manner similar to that utilized in conventional heterodyne repeaters, the drop-out lead means 13 being connected to a utilization circuit 15 which may include a receiver and demodulator for local communication. I

There is shown at 16 a generator of any convenient design for generating a signal having a frequency different from the microwave frequency received at antenna 10, and the device 16 in addition to generating the signal of the second frequency may include means for amplitude modulating or frequency modulating the signal of the second frequency, the signal of the second frequency being made responsive to modulation to provide for insertion of channels, and to this end there is shown a block 17 labeled baseband channel and operatively connected to generator 16 by lead means 18. The modulated or unmodulated output of the generator 16 is supplied by lead means 19 to the aforementioned mixer 14. Whereas only one baseband channel is shown at 17, it should be understood that a number of channels may be provided with means for connecting each of the channels to the generator and modulator 16 to provide for modulation of the signal generated thereat.

The mixer 14 may be of conventional design; if the signal at 19 is unmodulated as to frequency and is designated AF, the output of the mixer on lead means has a frequency F plus or minus AF, where F is the frequency of the received signal on lead 13. This signal representing F plus or minus AF is supplied by the aforementioned lead means 29 to a variable microwave attenuator 21, which may be of any convenient design, the variable microwave attenuator 21 having a mechanical coupling link 22 thereto for adjusting the setting of the attenuator and the amount of attenuation in accordance with movement of the coupling or adjusting means 22. The coupling or adjusting means 22 is moved in response to action of a moving means 23 shown in block form and which may be of any convenient design, such for example as a reversible motor and gear train, the moving means moving the arm or coupling 22 to increase or decrease the attenuation at 21 in accordance with control or energizing signals applied thereto by leads 24, 25 and 26 from a servo amplifier and reference voltage generator shown in block form at 27 andhereinafter to be more fully described.

The output of the variable microwave attenuator 21 is supplied by lead means 28 to a power klystron shown in block form in FIG. 1 at 29 and shown in more detail in FIG. 2, the output of the power klystron 29 be ing applied by conducting means 30, which may be waveguide means, to a transmitting antenna 31. Coupled to the conducting means 30 is a pickup means 32 for picking up a small portion of the energy in the conducting means 3%) and applying the picked up energy by way of lead 33 to a power monitor device 34, which may be a rectifier, and which provides on lead 35 a substantially direct current voltage having an amplitude which varies in accordance with variations in the energy picked up at 32 and accordingly with variations in the energy in the waveguide means 30, which is proportional to the power output of klystron 29. It will be understood that the direct current voltage or signal on lead 35 is supplied to a signal comparison circuit in the servo amplifier 27, and if the signal or voltage on lead 35 is above the reference voltage provided in the servo amplifier 27, the value of which may be adjusted at 42, then as previously mentioned the servo amplifier 27 applies signals on leads 24, 25 and 26 to cause the moving means 23 to move the adjusting means 22 to increase the attenuation in the attenuator 21 and reduce the power applied by lead 28 to the power klystron 29 thereby reducing the output thereof and reducing the signal or voltage on lead 35 to a value voltage on lead 35 obtained from the power monitor 34 is substantially equal to the reference voltage established in the servo amplifier 27.

Particular reference should be made now to FIG. 2 which shows very generally the internal arrangement of a typical two-cavity klystron, the glass envelope being shown at 36 with the input cavity being shown at 37 connected to the aforementioned lead means 28, and the output cavity being shown at 38 connected to the aforementioned output lead means 30. The coaxial cables 28 and 30 could of course be connected to suitable waveguides. The klystron 29 is seen to have a collector 39, a cathode 40 and accelerator grid 41. It will be understood that the klystron generally designated 29 and shown in detail in FIG. 2 has circuit means connected thereto, not shown, and including suitable sources of potential for applying the desired operating potentials to the various elements of the klystron 29. It will also be understood that the klystron may include other conventional elements such for example as a focussing electrode.

As will be readily understood by those skilled in the art, the cavities 37 and 38 of the klystron are themselves resonant chambers and accordingly each cavity has its own attenuation-versus-frequency characteristic, or a characteristic which might be described as a band pass characteristic. By suitable design the invention contemplates the use of a cavity at 38 having for example a 3 decibel bandwidth over a range of for example 30 to 40 megacycles. The bandwidth characteristics of the klystron amplifier 29 accordingly provide discrimination against unwanted signals, and the resonant characteristics of the cavities 37 and 38 prevent spurious output signals from being transmitted by the antenna 31. Accordingly, the necessity for elaborate, complex and expensive filtering circuits and band-pass circuits is obviated with an accompanying decrease in the size and complexity of the repeater equipment. Also, as previously mentioned, the filtering circuits of conventional repeaters introduce losses which must be overcome by providing additional amplification.

There has been provided, then, apparatus well suited to accomplish the aforedescribed objects of the invention, which are to provide a simplified wide band microwave repeater. The microwave attenuator 21 controlled by the power monitor 34 prevents overdriving the power klystron 29 and safeguards constant level of the output at the point where some limiting takes place in the last cavity 38 of the klystron. As previously stated, the first klystron 12 is a low-noise klystron which is provided to offset to some degree the usual high noise figure of a power klystron.

A gain of, for example, 121 decibels is preferably provided in the two klystron amplifiers 12 and 29; the first klystron 12 may provide a gain of 30 decibels, while the power klystron may easily provide a gain of 91 decibels making a total of 121. This gain is desirable to overcome the losses in the circuits which may include, for example, the path loss, which may be 60 decibels, a fading margin which may be 50 decibels, a feeder loss which may be 3 decibels, and a frequency conversion loss in the mixer 14 which may be, as previously stated, 8 decibels.

As will be understood, one of the frequency components F +AF, or F -AF may be substantially eliminated in the resonant cavities of the klystron 29.

It will be seen that the repeater of FIG. 1 is a relatively simple circuit, that the amplifier chain includes only two klystron tubes, and that no elaborate filtering or band-pass equipment is utilized. The AP generator and modulator 16 may be of conventional design and need not be too bulky because of the low level at which signals are mixed in the mixer 14.

The circuit of FIG. 1 has the further advantage that external filtering before and after reamplification is not required, the aforementioned resonant characteristics of the cavities 37 and 38 at least in part eliminating the need for such external filtering before and after amplification.

Other moving arrangements for adjusting the setting of attenuator 21 could be employed if desired.

Any suitable means, not shown, may be provided for energizing the heating means for the cathode 4%) of klystron 29.

Whereas for ease of illustration only two cavities are shown in the klystron 29, FIG. 2, it should be understood that any suitable number, for example, five could be used if desired.

Klystron 12 may be replaced by a parametric amplifier if desired.

Whereas the invention has been shown and described with respect to a preferred embodiment thereof which gives satisfactory results, it should be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

I claim as my invention:

1. Microwave repeater apparatus comprising, in combination, receiving antenna means, low noise klystron amplifier means having the signal of the receiving antenna means applied thereto, mixer means having the output of the low noise klystron amplifier means applied thereto, the receiving antenna means receiving a microwave signal of frequency F, generator means for applying to the mixer means a signal having a frequency AF whereby the mixer means provides an output signal having frequency components of F plus AF and F minus AF, variable microwave attenuator means adapted to have the attenuation therein varied in accordance with movement of an adjusting means and having the output of the mixer means applied thereto, power klystron means operatively connected to the variable microwave attenuator means and having the output signal of the variable microwave attenuator means supplied thereto, said power klystron means including a klystron with at least first and second resonant cavities, each of said first and second resonant cavities having a predetermined frequency-attenuation characteristic, said first and second resonant cavities substantially eliminating a selected one of the frequency components F plus AF and F AF, the signal to be amplified being applied to the first resonant cavity, transmitting antenna means, means connecting the transmitting antenna means to the second resonant cavity, power monitor means operatively connected to said means connecting the transmitting antenna means to the second resonant cavity, servo amplifier and reference signal obtaining means operatively connected to the power monitor means, and moving means operatively connected to the servo amplifier means to have the output of the servo amplifier means supplied thereto, said moving means being operatively connected to the adjusting means of the attenuator means, said moving means and servo amplifier means adjusting the value of the attenuation to increase the value thereof when the output of the power monitor means exceeds a predetermined value in accordance with the value of the reference signal, said servo amplifier means and moving means adjusting the attenuator means to decrease the attenuation therein when the output of the power monitor means falls below a predetermined value established by said reference signal.

2. Apparatus according to claim 1 including in addition baseband channel means operatively connected to said AF signal generator, said AF signal generator being additionally characterized as constructed and arranged to use the signal from the baseband channel to amplitude modulate the signal having a frequency AF to thereby provide for communication signal insertion in the microwave repeater apparatus.

3. A microwave repeater circuit comprising, in combination, means for receiving a mircowave signal of a first frequency, low noise klystron amplifier means for amplifying the signal of said first frequency, mixer means operatively connected to the low noise klystron amplifier means to have the output thereof applied thereto, means for generating a signal having a second frequency different from said first frequency, said generating means being connected to said mixer means, said mixer means providing a mixer output signal having two frequency components equal to the first frequency plus the second frequency and to the first frequency minus the second frequency, variable microwave attenuator means operatively connected to the mixer means to receive the output therefrom, power klystron means having first and second resonators, the first resonator being connected to the microwave attenuator means to receive the output therefrom, transmitting antenna means, said transmitting antenna means being connected to the second resonator of the power klystron means to receive the amplified output of the power klystron means, power monitor means operatively connected to said power klystron means for providing a signal proportional in amplitude to the power output of the power klystron means, and servo amplifier means including moving means operatively connecting the power monitor means to the variable microwave attenuator means for automatically adjusting the attenuation in accordance with the variations in the output of the power monitor means in a manner which tends to maintain the output of the power klystron means constant.

4. Apparatus according to claim 3 including in addition baseband channel means operatively connected to the means for generating a signal having a second frequency, and in which said means for generating a signal having a second frequency is additionally characterized as including means for amplitude modulating the signal of second frequency in accordance with the output provided from the baseband channel means.

5. Apparatus according to claim 3 wherein the first and second resonators of the power klystron means are additionally characterized as having predetermined resonant frequency band pass and attenuation characteristics to provide discrimination against unwanted signals including one of said frequency components and to prevent spurious output signals transmitted by said transmitting antenna means.

6. Microwave repeater apparatus comprising, in combination, microwave signal receiving means including amplifying means, frequency converting means operatively connected to the microwave receiving means for converting the frequency of the energy received thereby to at least a second frequency which differs from the first frequency by a predetermined amount, variable attenuator means operatively connected to said frequency converting means and having the output thereof applied thereto, power klystron amplifier means operatively connected to the variable attenuator means to receive the output therefrom, said power klystron amplifier means having first and second resonators, said first and second resonators being constructed and arranged to provide a band-pass of the desired width and attenuation characteristic for the radio frequency signal of said second frequency to be amplified in the power klystron means, transmitting antenna means operatively connected to the power klystron means to receive the output therefrom, and power regulating means including power monitor means connected to the output of the power klystron means and to said variable attenuator means, said power regulating means being constructed and arranged to maintain the output of the power klystron means substantially constant irrespective of variations in the input to the variable attenuator means.

7. A microwave repeater circuit comprising, in combination, means for receiving a microwave signal of a first frequency, means connected to said receiving means for converting the received signal to a signal having a second frequency different from the first frequency, klystron amplifier means, transmitting antenna means, said klystron amplifier means connecting the transmitting antenna means to the means for obtaining a signal of second frequency, said klystron amplifier means having first and second resonators, said first and second resonators having predetermined band-pass and frequency attenuation characteristics to provide discrimination against unwanted signals and prevent spurious output signals from reaching the transmitting antenna means, and means operatively connected to the klystron amplifier means for maintaining the power output of the klystron amplifier means substantially constant irrespective of variations in the output of the means for obtaining the signal of the second frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,446,572 Bull Aug. 10, 1948 2,735,933 Pierce Feb. 21, 1956 2,897,274 Forbes July 28, 1959 

